On the morning of Feb. 18, noise and vibrations were reported, with hydrocarbons confirmed shortly afterward in the process module.
A 2-mm (0.08-in.) wide crack had opened up more than 90% of the circumference of a 2-in. pipeline. Condensate had leaked from the line, with gas released at a rate thought to be around 8 kg/sec.
The volume of condensate from the leak is estimated at 4 cu m (141 cu ft).
No personnel were present in the area at the time, but there could have been a fatality if someone had been exposed to the leak, with potential for a major incident if the gas had ignited.
Analysis suggests the crack was caused by fatigue and overload. An under-dimensioned level valve led to vibrations both in the valve and the surrounding piping system during regular plant operation.
The vibrations resulted in loss of level valve control, leading to repeated powerful vibrations and strokes in the piping system that exceeded the design capacity.
No material defects, metallurgical irregularities or welding defects have come to light, although the team believes that a full pipeline break could have resulted.
The gas detectors recorded the leak, ignition sources were disconnected and the deluge system started automatically, as did the pressure relief system and the emergency shutdown system.
Øystein Arvid Håland, the company’s senior vice president of safety and sustainability in the Development and Production Norway division, said: “Statoil is working systematically on gas leak prevention, and the learnings from this incident shall be translated into specific actions. We must ensure that these efforts help prevent future incidents.”